The early synthesis method for olefin polymer involves preparing a boron compound of cyclopentenone and using the Suzuki-coupling reaction, as shown in the following Scheme 1. This method is, however, problematic in that the boron compound is hard to synthesize, making the synthesis method unsuitable for large-scaled manufacture, and that only a limited range of boron compounds can be prepared, consequently with difficulty in diversification of cyclopentadienyl ligands (Organometallics 2006, 25, 2133; Dalton Trans. 2006, 4056; Organometallics 2006, 25, 5122; Dalton Trans. 2007, 4608; Organomet. Chem. 2008, 693, 457; J. Organomet. Chem. 2006, 691, 5626; Korean Patent Registration No. 10-843603; Korean Patent Registration No. 10-0789241; Korean Patent Registration No. 10-0789242; and Korean Patent Registration No. 10-0843603).

To solve this problem, there has been developed a new synthesis method given by the following Scheme 2. The synthesis method in the Scheme 2 advantageously provides an approach to preparing the desired ligand in a single step and introduces a variety of 5-membered cyclic pi-ligands, such as indenyl or fluorenyl (Organometaalics, 2008, 27, 3907).

The following compound 1 or 2 prepared by this method is superior to the conventional CGC([Me2Si(η5-Me4C5)(NtBu)]TiCl2) catalyst developed by Dow Chemical Corp. in terms of catalytic activity and copolymerization characteristic, showing the possibility of its use in the commercial manufacture process (Organometallics, 2007, 27, 6685; Macromolecules, 2008, 42, 4055; Macromolecules, 2010, 43, 725; Korean Patent Registration No. 820, 542; Korean Public Patent No. 08-0065868; and Korean Patent Registration No. 906,165). More specifically, the amido ligand is combined with the ortho-phenylene ligand to form a condensed ring, which reduces the steric hindrance at the reaction site of titanium to enhance reactivity.

Besides, transition metal compounds of 5-membered cyclic pi-ligands fused with a heterocyclic compound containing nitrogen or sulfur atom(s), and an olefin polymerization reaction using the transition metal compounds have been occasionally reported. But, there has never been a report on the transition metal compounds coordinated with 5-membered cyclic pi-ligands fused with a heterocyclic compound among those compounds having a condensed ring formed with an amido ligand and an ortho-phenylene ligand like compound 1 or 2 (J. Am. Chem. Soc., 1998, 120, 10786; J. Am. Chem. Soc., 2001, 123, 4763; Macromol. Chem. Phys., 2004, 205, 302; Angew. Chem. Int. Ed., 2009, 48, 9871; Organometallics, 2002, 21, 2842; J. Am. Chem. Soc., 2004, 126, 17040; Macromol. Chem. Phys., 2004, 205, 2275; Macromol. Chem. Phys., 2005, 206, 1405. Organometallics, 2004, 23, 344; J. Am. Chem. Soc., 2003, 125, 10913; Organometallics, 2009, 28, 6915; J. Organomet. Chem., 2005, 690, 4213; and U.S. Pat. No. 6,451,938).
Sustainable attempts have been made in the fields of academy and industry to develop homogenous Ziegler-Natta catalysts since Prof. Kaminsky developed the homogeneous Ziegler-Natta catalyst using a Group 4 metallocene compound activated with a methylaluminoxane co-catalyst in the late 1970's (Kaminsky et al., Dalton Trans., 2009, 8803). It is the advantage claimed for the homogenous Ziegler-Natta catalysts over the heterogeneous Ziegler-Natta catalysts that the homogeneous Ziegler-Natta catalysts are excellent in α-olefin incorporation in ethylene/α-olefin copolymerization and provide a uniform α-olefin distribution. The conventional heterogeneous catalysts in ethylene/α-olefin copolymerization not only provide a low quantity of α-olefin incorporation but cause the α-olefin incorporation to occur primarily in the polymer chain with low molecular weight only. On the other hand, the disadvantage of the homogeneous catalysts is that they cannot provide a polymer with high molecular weight. In contrast to the conventional heterogeneous Ziegler-Natta catalysts which are used to form a polymer chain with high molecular weight, the homogeneous catalysts can be used only to produce a polymer chain with a molecular weight of no more than about 100,000. With low molecular weight, the polymers encounter a limitation in development of their usage, such as being inapplicable to the products required to have high strength. For that reason, the conventional heterogeneous Ziegler-Natta catalysts have been used in the industrial manufacture of polymers, and the use of the homogeneous catalysts is confined to the manufacture for some grades of polymer. It is therefore the ultimate object to overcome such a fundamental limitation by developing a homogeneous catalyst excellent in α-olefin reactivity and capable of producing polymers with high molecular weight.
In an attempt to solve the problems with the prior art, the inventors of the present invention have discovered a novel ligand in which an amido ligand is linked to an ortho-phenylene ligand to form a condensed ring, and a 5-membered pi-ligand combined with the ortho-phenylene ligand is fused with a heterocyclic thiophene ligand, and found it out that the catalyst comprising a transition metal compound prepared from the novel ligand has higher catalytic activity and provides a polymer with higher molecular weight than the catalyst not fused with a heterocyclic thiophene ligand, thereby completing the present invention.